From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751557AbdAWVKl (ORCPT ); Mon, 23 Jan 2017 16:10:41 -0500 Received: from mga07.intel.com ([134.134.136.100]:26714 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751340AbdAWVKe (ORCPT ); Mon, 23 Jan 2017 16:10:34 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.33,275,1477983600"; d="scan'208";a="34426962" Subject: Re: [tip:x86/urgent] x86/fpu: Set the xcomp_bv when we fake up a XSAVES area To: Yu-cheng Yu References: <1485075023-30161-1-git-send-email-haokexin@gmail.com> <20170123165529.GA4996@test-lenovo> <2be814b7-9fd6-7955-b4e3-6ecb4ef76052@linux.intel.com> <20170123205725.GA3920@test-lenovo> Cc: fenghua.yu@intel.com, dvlasenk@redhat.com, peterz@infradead.org, oleg@redhat.com, mingo@kernel.org, linux-kernel@vger.kernel.org, brgerst@gmail.com, luto@kernel.org, bp@alien8.de, jpoimboe@redhat.com, haokexin@gmail.com, hpa@zytor.com, quentin.casasnovas@oracle.com, tglx@linutronix.de, torvalds@linux-foundation.org, riel@redhat.com, linux-tip-commits@vger.kernel.org From: Dave Hansen Message-ID: <90b0fbee-273b-31c2-6fe9-228f00c0a205@linux.intel.com> Date: Mon, 23 Jan 2017 13:10:20 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <20170123205725.GA3920@test-lenovo> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/23/2017 12:57 PM, Yu-cheng Yu wrote: > On Mon, Jan 23, 2017 at 09:23:06AM -0800, Dave Hansen wrote: >> On 01/23/2017 08:55 AM, Yu-cheng Yu wrote: >>>> The best fix here would be not to paper over the issue in the copy >>>> function but find where it got clobbered, or where some initialization >>>> code failed to set it. >>> >>> Someone else reported different issues from the same bug and a different >>> patch was just tested OK this morning. I think that adding xfeatures bits >>> to xcomp_bv should have been done in fpstate_init(). >> >> Right. So where did it get cleared out? > > It is not set until a task triggers XSAVES. We did not set it in fpstate_init() > because there is no valid data at the time. The code is: > void fpstate_init(union fpregs_state *state) > { > if (!static_cpu_has(X86_FEATURE_FPU)) { > fpstate_init_soft(&state->soft); > return; > } > > memset(state, 0, fpu_kernel_xstate_size); > > /* > * XRSTORS requires that this bit is set in xcomp_bv, or > * it will #GP. Make sure it is replaced after the memset(). > */ > if (static_cpu_has(X86_FEATURE_XSAVES)) > state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT; That seems to set it unconditionally. What am I missing?